Electric Generating Units, Capacity

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Share Of Purchased Power

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Amount of distribution received from equity method investee for return on investment, classified as operating activities. Excludes distribution for return of investment, classified as investing activities.

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The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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The proportionate share of interest (percent) in a jointly owned utility plant.

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CONSOLIDATED ENTITIES AND EQUITY METHOD INVESTMENTS - SEGCO Equity Method Investments Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($) MW	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Alabama Power
Jointly Owned Utility Plant Interests [Line Items]
Ownership percentage, equity method investment	50.00%
Percent ownership	14.00%
Alabama Power \| SEGCO
Jointly Owned Utility Plant Interests [Line Items]
Total megawatt capacity (in MWs) \| MW	1,020
Share of purchased power	$ 67	$ 93	$ 102
Dividends paid by equity method investment	$ 12	14	18
Georgia Power
Jointly Owned Utility Plant Interests [Line Items]
Ownership percentage, equity method investment	50.00%
Georgia Power \| SEGCO
Jointly Owned Utility Plant Interests [Line Items]
Share of purchased power	$ 69	$ 95	$ 105
SEGCO \| Alabama Power
Jointly Owned Utility Plant Interests [Line Items]
Percent ownership	86.00%